Low-cost electrolyte for high-voltage sodium-ion battery

Abstract

The invention discloses a low-cost electrolyte for a high-voltage sodium-ion battery, the electrolyte comprises an organic solvent, a solute and additives, the organic solvent adopts a pure linear carbonic ester solvent, the solute adopts sodium hexafluorophosphate, and the additives comprise a film-forming additive, a flame-retardant additive and an overcharge protection additive; compared with the prior art, the electrolyte has the advantages that the electrolyte adopting the pure linear carbonic ester solvent and sodium hexafluorophosphate as a sodium source is applied to sodium metal, and when the electrolyte is applied to a P2-phase material, the electrolyte can stably work at 4.5 V and exert high capacity, and the electrolyte has high and good high-voltage stability along with the increase of the chain length. Wherein the circulation retention rate of DEC can be maintained at 94.94% at 4.5 V, 2C and 300 circles. Therefore, the high-pressure stability can be remarkably improved by increasing the chain length of the linear ester.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion battery electrolytes, in particular to a low-cost electrolyte for high-voltage sodium ion batteries. Background Art

[0002] High-voltage sodium metal batteries are considered to be one of the most promising energy storage systems because of their abundant sodium resources, high theoretical capacity and low potential. However, at the same time, there are a series of problems with the sodium metal negative electrode: uneven sodium deposition / dissolution, and continuous cracking of the solid electrolyte interface phase (SE I) caused by complex interfacial reactions. These problems accelerate the capacity decay of sodium metal batteries. Although there are currently a variety of electrolyte improvement strategies applied to high-voltage sodium metal batteries. For example: new solvents / additives, local high-concentration electrolytes, and high-concentration electrolytes, the cost is generally high, which is not conducive to commercial applications. In addition, the concentration of high-concentration electrolytes is high, the interaction force between positive and negative ions increases, ion migration is hindered, and the viscosity is large. Therefore, it is not conducive to the wetting of positive and negative electrode plates and diaphragms, and reduces the capacity utilization of battery materials. Although the sodium salt concentration of the local high-concentration electrolyte is lower than that of the high-concentration electrolyte, it is still a problem faced by the high-concentration electrolyte, and the current diluents are relatively single and mostly fluoroethers. Fluorinated ether dissolution is often highly toxic and seriously pollutes the environment. Therefore, commercial applications are also limited.

[0003] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the above technical defects and provide a low-cost electrolyte for high-voltage sodium ion batteries, which uses a pure linear carbonate solvent and sodium hexafluorophosphate as a sodium source electrolyte for sodium metal. Compared with the high-concentration / local high-concentration electrolyte system, this electrolyte system has changes in cost, ion conductivity, wettability, etc. When applied to P2 phase materials, it can work stably at 4.5V and exert its higher capacity. At the same time, it has good high-voltage stability as the chain length increases. Among them, DEC can maintain a cycle retention rate of 94.94% at 4.5V, 2C, and 300 cycles. It can be seen that the high-voltage stability can be significantly improved by increasing the chain length of linear esters.

[0005] In order to solve the above problems, the technical solution of the present invention is a low-cost electrolyte for high-voltage sodium ion batteries: the electrolyte includes an organic solvent, a solute and an additive, the organic solvent is a pure linear carbonate solvent, the solute is sodium hexafluorophosphate, and the additive includes a film-forming additive, a flame retardant additive, and an overcharge protection additive.

[0006] Furthermore, the pure linear carbonate solvent includes one or more combinations of diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0007] Furthermore, the film-forming additive includes one or more combinations of FEC, VC, 13-PS, PST, DTD and NaDFOB.

[0008] Furthermore, the method for preparing a low-cost electrolyte for a high-voltage sodium ion battery comprises the following steps:

[0009] Step 1: preparing raw materials, including organic solvents, solutes and additives;

[0010] Step 2, dissolving the solute, dissolving the solute in an organic solvent to form a basic solution;

[0011] Step 3, adding additives: adding additives to the basic solution;

[0012] Step 4: stirring and mixing: fully stirring the solution to form a uniform electrolyte;

[0013] Step 5: Filter and remove impurities to ensure the purity of the electrolyte;

[0014] Step 6: Performance testing;

[0015] Step 7: Packaging and storage.

[0016] Furthermore, the performance test includes a linear sweep voltammetry test, a cycle test and a rate test.

[0017] Furthermore, the concentration of sodium hexafluorophosphate in the electrolyte is 1 mol / L.

[0018] Furthermore, the volume fraction of the additive to the total volume of the solvent is 2%.

[0019] The advantages of the present invention compared with the prior art are:

[0020] 1. The present invention uses a pure linear carbonate solvent and sodium hexafluorophosphate as a sodium source electrolyte for sodium metal. Compared with the high-concentration / local high-concentration electrolyte system, this electrolyte system has changes in cost, ion conductivity, wettability, etc. It can be used in P2 phase materials to work stably at 4.5V and exert its higher capacity. With the increase of chain length, it has high high-voltage stability. Among them, DEC can maintain a cycle retention rate of 94.94% at 4.5V, 2C, and 300 cycles. It can be seen that the high-voltage stability can be significantly improved by increasing the chain length of linear esters. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the XRD diagram of the P2 phase positive electrode material of the present invention.

[0022] Figure 2 It is the LSV curve diagram of the present invention.

[0023] Figure 3 It is the long cycle graph of the present invention.

[0024] Figure 4 It is a magnification diagram of the present invention.

[0025] Figure 5 It is a cycle diagram of three embodiments of the present invention under a high voltage of 4.7V.

[0026] Figure 6 yes Figure 2 A partial enlarged view of . DETAILED DESCRIPTION

[0027] In order to make the contents of the present invention more clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0028] like Figure 1-5 As shown, a low-cost electrolyte for high-voltage sodium ion batteries, the electrolyte includes an organic solvent, a solute and an additive. The organic solvent is a pure linear carbonate solvent. The solvent has good solubility for sodium salts, can provide good ion transmission ability, and has a relatively stable structure, oxidation resistance, and high safety. The solute is sodium hexafluorophosphate, which has good ionic conductivity and thermal stability. The additives include film-forming additives and flame retardant additives, which are used to improve the flame retardant properties of the electrolyte, reduce the risk of battery fire, and overcharge protection additives to prevent battery overcharging and extend the service life of the battery.

[0029] The pure linear carbonate solvent includes one or more combinations of diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate. The film-forming additive includes one or more combinations of FEC, VC, 13-PS, PST, DTD, and NaDFOB. The additive undergoes a reduction reaction before the solvent molecules to form a dense, uniform, and thin SE I / CE I film on the surface of the positive and negative electrodes to protect the electrode materials. The concentration of sodium hexafluorophosphate in the electrolyte is 1 mol / L.

[0030] A method for preparing a low-cost electrolyte for a high-voltage sodium ion battery comprises the following steps:

[0031] Step 1: preparing raw materials, including organic solvents, solutes and additives;

[0032] Step 2: dissolving the solute, dissolving the solute in the organic solvent to form a basic solution; heating or stirring is required in this process to promote the dissolution of the solute;

[0033] Step 3, adding additives: adding additives to the basic solution;

[0034] Step 4: stirring and mixing: fully stirring the solution to form a uniform electrolyte;

[0035] Step 5: Filter and remove impurities to ensure the purity of the electrolyte;

[0036] Step 6: Performance testing;

[0037] Step 7: Packaging and storage: Pack the qualified electrolyte and store it under appropriate conditions to prevent its performance from changing.

[0038] The performance tests include linear sweep voltammetry test, cycle test and rate test.

[0039] Comparative Example 1

[0040] Cyclic ester is used as solvent, sodium hexafluorophosphate is used as solute, the concentration is 1M / L, fluoroethylene carbonate is used as additive, and the volume fraction of the additive to the total volume of the solvent is 2%. The above mixture forms an electrolyte system.

[0041] Comparative Example 2

[0042] A mixture of cyclic ester and linear ester is used as the solvent, the cyclic ester is PC, the linear ester is DMC, PC:DMC=1:1, the solute is sodium hexafluorophosphate, the concentration is 1M / L, the additive is fluoroethylene carbonate, and the volume fraction of the additive to the total volume of the solvent is 2%. The above mixture forms an electrolyte system.

[0043] Comparative Example 3

[0044] A mixture of cyclic ester and linear ester is used as the solvent, the cyclic ester is PC, the linear ester is DEC, PC:DEC=1:1, the solute is sodium hexafluorophosphate, the concentration is 1M / L, the additive is fluoroethylene carbonate, and the volume fraction of the additive to the total volume of the solvent is 2%. The above mixture forms an electrolyte system.

[0045] Embodiment 1

[0046] Pure linear ester is used as solvent, the pure linear ester is DMC, the solute is sodium hexafluorophosphate, the concentration is 1M / L, the additive is fluoroethylene carbonate, the volume fraction of the additive to the total volume of the solvent is 2%, and the above mixture forms an electrolyte system.

[0047] Embodiment 2

[0048] Pure linear ester is used as solvent, pure linear ester is DEC, solute is sodium hexafluorophosphate, concentration is 1M / L, additive is fluoroethylene carbonate, volume fraction of additive is 2% of total volume of solvent, and the above mixture forms electrolyte system.

[0049] The above comparative examples and embodiments were subjected to linear sweep voltammetry tests, cycle tests and rate tests, and it was found that the materials used in the P2 phase can work stably at 4.5V and exert their higher capacity. With the increase of chain length, it has good high-voltage stability. Among them, DEC can maintain a cycle retention rate of 94.94% at 4.5V, 2C, and 300 cycles. It can be seen that the high-voltage stability can be significantly improved by increasing the chain length of the linear ester.

[0050] This description is not restrictive, and the drawings are only one of the embodiments of the present invention. In short, if ordinary technicians in this field are inspired by it and design structural methods and embodiments similar to the technical solution without creativity without departing from the purpose of the invention, they should all fall within the protection scope of the present invention.

Claims

1. A low-cost electrolyte for high-voltage sodium-ion batteries, characterized in that: The electrolyte includes an organic solvent, a solute and an additive. The organic solvent is a pure linear carbonate solvent, the solute is sodium hexafluorophosphate, and the additive includes a film-forming additive, a flame retardant additive and an overcharge protection additive.

2. A low-cost electrolyte for high-voltage sodium ion batteries according to claim 1, characterized in that: The pure linear carbonate solvent includes one or more combinations of diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate.

3. A low-cost electrolyte for a high-voltage sodium ion battery according to claim 1, characterized in that: The film-forming additives include one or more combinations of FEC, VC, 13-PS, PST, DTD and NaDFOB.

4. A method for preparing a low-cost electrolyte for a high-voltage sodium ion battery according to claims 1-3, characterized in that: The following steps are involved: Step 1: preparing raw materials, including organic solvents, solutes and additives; Step 2, dissolving the solute, dissolving the solute in an organic solvent to form a basic solution; Step 3, adding additives: adding additives to the basic solution; Step 4: stirring and mixing: fully stirring the solution to form a uniform electrolyte; Step 5: Filter and remove impurities to ensure the purity of the electrolyte; Step 6: Performance testing; Step 7: Packaging and storage. The method for preparing a low-cost electrolyte for a high-voltage sodium ion battery according to claim 4 is characterized in that the performance test is a linear sweep voltammetry test, a cycle test and a rate test.

5. A low-cost electrolyte for high-voltage sodium ion batteries according to claim 1, characterized in that: The concentration of the sodium hexafluorophosphate in the electrolyte is 1 mol / L.

6. A low-cost electrolyte for high-voltage sodium ion batteries according to claim 1, characterized in that: The volume fraction of the additive to the total volume of the solvent is 2%.

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